What is the number of diploid chromosomes in humans?

When radioactive thymine is added to the medium during the synthesis of new $DNA$ in human cells,which of the following chromatids will become radioactive in cells that enter the phase immediately upon contact with radioactive thymine?

$(1)$ Definition / Explanation: Mitosis
$(2)$ Definition / Explanation: Meiosis

Mitotic crossing over takes place in

Cell division occurs . . . . . . in plants and . . . . . . in animals.

Based on the figures given below,select the option that shows the correct sequence of cell division.